Mastaba wrote on Sep 4, 2012, 15:56: Wait, but a GeForce 8800GT is not a DirectX 11 part. So the game can run without the DirectX 11 specific features. So, there must be at least a DirectX 10 fallback. So really what they meant to say is that since the game requires at least DirectX 10 Windows XP is not supported.
DirectX 11 (the software API) is backwards compatible with DirectX 10 hardware. The API will automatically enable/disable features based on hardware support.
The DirectX 9/XP cut-off is due to the fact that DX10 was essentially re-engineered from the ground-up to support the overhauled driver model (WDDM) which was first introduced in Vista.